Preheat oven to 375°. Lightly spray a 2-quart baking dish with cooking spray.
In a small skillet, melt butter over medium heat. Add onion and bell pepper; cook, stirring frequently, until onion is tender, 3 to 4 minutes. Stir in flour; cook for 1 minute. Remove from heat.
In a medium bowl, stir together onion mixture, sour cream, salt, and pepper. Fold in potatoes and half of cheese. Spoon mixture into prepared pan, and cover with foil.
Bake for 40 minutes. Uncover, top with remaining cheese, and bake until cheese is melted, about 15 minutes more. Let stand for 10 minutes before serving.
Recipe by Paula Deen Magazine at https://pauladeenmagazine.com/cheesy-hash-brown-casserole-recipe/